The theory of the race track microtron is well known to those skilled in the art.
Evidently different parts of a race track microtron may be designed in more or less different ways. Generally, however, a race track microtron comprises a linear accelerator placed between deflecting magnetic fields. The linear accelerator increases the energy of passing electrons and the deflecting magnetic fields cause the electrons to follow successively greater orbits passing trough the linear accelerator a number of times.
The deflecting magnetic fields may be two generally uniform fields each deflecting incoming electrons 180.degree. (see P. M. Lapostolle "Linear Accelerators", North-Holland Publishing Company, Amsterdam 1970, especially page 559).
For various reasons the two deflecting magnetic fields may be made non-uniform instead of uniform (see H. R. Froelich and J. J. Manca "Performance of a multicavity racetrack microtron", IEEE Transactions on Nuclear Science, Vol. NS-22, No. 3, June 1975, pages 1758-1762).
Instead of two deflecting fields, each deflecting incoming electrons 180.degree., four deflecting fields, each deflecting incoming electrons 90.degree., may be used (see page 555 of the Lapostolle reference cited above).
In addition to deflecting magnetic fields correction magnetic fields may be used in the vicinity of the deflecting magnetic fields for stabilizing particle orbits in a race track microtron (see H. Babic and M. Sedlacek "A method for stabilizing particle orbits in the race track microtron", Nuclear instruments and methods, Vol. 56, 1967 , pages 170-172 and L. M. Young, "Experience in recirculating electrons through a superconducting linac", IEEE Transactions on Nuclear Science, Vol. NS-20, No. 3, 1973, pages 81-85, especially FIG. 2).
When mounting and assembling at least some prior art race track microtrons, problems might occur with the positioning and orientation of the magnetic field systems in relation to each other and to the linear accelerator. The reason is that inevitable imperfections in the magnetic systems from their manufacture and imperfections in the positioning and orientation of the magnetic systems and linear accelerators cause an accumulating error in the position of the orbits, whereby optimum performance of the microtron is difficult or impossible to achieve. This error is difficult to impossible to calculate with accuracy in advance but will appear when the mounted and assembled microtron is run.
One way to overcome this problem is to make the position and/or orientation of at least one magnet system and eventually the linear accelerator turnable during operation of the race track microtron. This, however, is difficult to make with large and heavy microtrons and with such smaller and simpler microtrons where there is a need for turning the entire microtrons due to the field of use of the accelerated electrons. Furthermore an efficient extraction of accelerated electrons are made more difficult and complicated when parts of the microtron is turned during operation.
Another way to overcome the problem is to incorporate in the microtron in the field free space between the deflecting magnet systems a new magnetic system creating a generally uniform magnetic field transverse to the plane of the orbits and having a generally wedgeshaped area of distribution in the plane of the orbits (see. R. Alvinson and M. Eriksson "A design study of a 100 MeV race track microtron/pulse stretcher accelerator system", TRITA-EPP-76-07 and LUSY 7601, Royal Institute of Technology, Stockholm 1976, especially pages 6, 29 and 35-36).
A third way to overcome the problem would be to incorporate in the microtron in the field free space between the deflecting magnet systems extra focusing devices such as quadrupole magnets and/or deflecting devices such as dipole magnets each affecting the straight parts of one or a few orbits or the common part of all orbits (see P. Axel et al., "Microtron using a superconducting electron linac", IEEE Transactions on Nuclear Science, Vol. NS-22, No. 3, June 1975, pages 1176-1178 and H. Herminghaus et al., "The design of a cascaded 800 MeV normal conducting C.W. race track microtron", Nuclear instruments and methods, Vol. 138, 1976, pages 1-12, especially FIGS. 8-10 with corresponding text). This way would be rather complex if good results are to be achieved wanted and will also make efficient extraction of accelerated particles from orbits more difficult or complicated.